A non-A, non-B antigen will be sought in serums from patients with acute or chronic non-A, non-B hepatitis by reacting them with convalescent phase serums in radioimmunoassays. In addition, plasma units derived from either donors implicated in non-A, non-B hepatitis or patients with acute or chronic non-A, non-B hepatitis will be ultracentrifuged. The pellet derived by ultracentrifugation will be reacted against a radiolabeled IgG fraction obtained from patients convalescent from non-A, non-B hepatitis in a solid phase radioimmunoassay system. Potential convalescent sera will first be prescreened for antibody activity by the RIA system established by Dr. Wolfgang Arnold in Mainz, West Germany. In addition, cytoplasmic ultrastructures will be isolated and purified from NANB-infected chimpanzee liver and these structures used to induce NANB antibodies in an animal model or hybridoma system.